Method of and tool for cutting screw threads



Jan. 17, 1928. 1,656,599

'T. PETERSEN METHOD OF AND -TOOL FOR CUTTING SCREW THREADS Filed Aug. 25, 1924 Patented Jan. 17,1923.

UNITED STATES 1,656,599 PATENT OFFICE.

rnonvm rn'rnnsmr, or 1mm, rmsrnvmm, nssren'on r nnnn unnurac'ronme serum, or ERIE, rnmrsrnvsms, acoaronarron or rnnnsrnvama.

' METHOD or AK!) moonron Application filed August 25, 1924. Serial 110. 733,947.

Screw threads are ordinarilycut by a succession of screw cutting teeth on dies or taps eachsucceeding tooth cutting a portion 0 the opposing slopes of the thread. The chip from such a cut is V-shaped in cross section and consequently ofiers quite a resistance to the cutting movement. The chip by reason of its shape is usually broken into ve short lengths. With tapered threads, suc as pipe threads, each succeeding tooth. takes a slight shaving so that this V-shaped chip exten s througlhquite a number of succeeding threads. he difiiculty, therefore, is aggravated in cutting tapered threads. It 5 is a so difiicult to start the cutting tool, particularly dies, and it is common to provide such tools with a lead screw to assure the proper starting of the die.

- According to the present invention I form an initial screw thread of ap roximately the lead of' the final crests but 0 not complete the troughs of these 'screw threads. .On the contrary I do not cut out the'troughs of these threads and in effect, therefore, form an intermediate thread so that there is in the starting or'throat of the die a double screw thread. Such a thread will readily engage a pipe, or part to be cut and start the tool. One reason for thisis that there are a greater number of teeth adapted to engage the pi and with the taper teeth at exactly the r1 diameter are more certain to be available o .making the initial engagement. While the metal removed informing these thin threads may be V-shaped in cross section the depthof the trough is so slight that the cross section of the chip does not present the jance of a cross section'of a full-dc th chip". After this initial double t 19' formed I remove practicall in a single cutting at the base thei'nterm 'ate thread 188V? mg a-trough with a substantially flat bottom. Succeeding teeth then remove the.

metal from the bottom of the tro h by succeeding cuts, the ends of this in line-with the slo of the final In gs we a 0111: of eep caifssrgection iaavoiilnll sot att eturmng' 'o in'cuflang' e thread is verymuch reduced.

In cutting tapered'thre eds as pipe threads, particularly where the dies are of g a thickness to cut the entire ipe thread wlth- .out the ad'ustment of the 'e-the cuts exten over so many as to ofier verygreatresistance. Iprefagthereforqin taper of the crest o .removed, preferably by a single cut of a cutting out the intermediate thread to cut it out with slopes which will form a crest approximately in line with the succeeding teethin other words, make the crest of this tooth extended inwardl from the line of the the finished teeth. The effect of this is to relieve the teeth'immediately following this in the die from the necessity of cutting the side slopes of the threads adjacent to their crests, thus reducing the number of teeth engaged in cutting the side slopes and thus reducing the effort necessary to turn the die.

I have illustrated the invention as operatin in connection with a die asiolldwsz- 1 ig. 1 shows an elevation of a ie.

Fig. 2 a side elevation of one o the cutting faces of the 'chaserson the die.

Figs. 3, 4, 5 and 6 numbers 1, 2, 3 and 4 chasers arranged with succeeding teeth in alinement as they engage the work succes: sively.

A marks a die and B a section of pipe bein cut. nitial teeth 5 of the lead of the final thread are formed at the throat of the finalcrests cut by the teeth 6. Intermediate crests 8 are formed between the crests 7, these crests being in efiect intermediate threads formed in the troughs of the threads with the crests 7. When the teeth have made their cuts topractically the depth of these teeth and have thus fully started the die the intermediate thread 8 1s completely tooth '9 as shown in the chaser 2. Following the tooth 9 successive teeth 10,11, 12, 13, 14

15 and 16 take small flat cuts as indica in dotted lines at 17 and 18 in F1g. 2. At the complet of these cutsa V-shaped troughis formed. Followin this the teeth 6 finish the thread and w ere a tapered thread is to be formed the crests of the thread formed by the teeth 6 are on a taper. 'It be observed, therefore, that the main cut of the thread is made by the teeth 5 and by the teeth 9, succeeding teeth taking cuts of shallow cross section. The teeth '6 only make the full V-shaped cuts and. these onlyto a depth 11 ry to give the thread no the desired taper where a tapered thread is cut.

While the tooth 9 removes the entire thread 8, this thread'at this point is so sha'l low that the cross sectional depth of the chip is comparatively sli ht and there is slight resistance. I pret ier to make the slopes of this tooth such as to form a crest at 19 inwardly between the line of the taper formed by the crests 20 of the teeth 6. Preferabl the crest 19 is extended inwardly to that o the crest 21 of the first full tooth 6. As a result of continuing the-crests 19 inwardly the base of the slopes of the tooth 9 will be slightly wider apart than the standard tooth 6 as clearly indicated in Fig.

2. The effect of this is to not only remove the intermediate thread 8 with the tooth 9 but also to remove the slopes'of the thread 7 so that the succeeding tooth or teeth make no out or very little cut on the outer slopes next .the crests of the thread being out. Thus the cuts made by the teeth 10, 11, 12,

13, 14, 15 and 16 have only the flat cross sectional chip, these teeth bein relieved of slope cutting except to the dept of the flat which consists in forming of the desired lead and with crests approxichi In this way the effort necessary to ma e the total cut is reduced.

What I claim as new is 1. The method of forming screw threads which consists informin an initial thread of the desired pitch an with a crest approximately the final pointed crest and a single intermediate po1nted thread of the same pitch cutting off the intermediate thread and then completing the trough by flat cuts.

2. The method of'forming screw threads which consists in forming an initial thread of the desired lead and with a crest approximatel the final crest and an intermediate threa of the same pitch cuttin ofi the intermediate thread and then comp sting the trough by successive substantially flat cuts extending across the trou h and following the thread slope at the si es of the trough.

3. The method of forming screw threads which consists in forming an initial thread of the desired lead and with crests approximatin the final crests and an intermediate threa of the same pitch, cutting ofi the intermediate thread at its base and complet ing the trough.

4. The method of forming screw threads which consists in forming an initial thread of the desired lead and with crests approxim'atin the final crests and an intermediate threa of the same pitch, on ofi the intermediate thread at its base an completing the trough by substantially flat cuts extending across the trough and following the slope of the thread at the sides of the trough.

5. The method ofiormingscrew threads 'with a final crest approximatin an initial threadmating the final crests and an intermediate thread of the same pitch, cutting of! the intermediate thread and the slopes leading to the intermediate thread, and completing the trough from which the intermediate thread is removed by substantially flat cuts extending across the trough.

6. A screw thread cutting tool having teeth cutting an initial thread on a taper with a final crest approximating the crest of the final thread said teeth forming an intermediate thread, a succeeding tooth cutting oif said intermediate thread, said cuttingofi tooth having guiding surfaces engagin the opposing slopes of the initial thread, an a succeeding tooth completing the trough.

7. A screw thread cutting tool havin initial thread cutting teeth forming initia threads with crests approximating the crests of the final thread and an intermediate thread, said tool having successive teeth cutting off the intermediate thread and teeth com leting the trough comprising successive teet making substantially flat cuts across the trough.

8. A screw thread cutting die having initial thread cutting teeth forming an initial thread with a crest following the crest of the final thread and an intermediate thread, a su cu toothcutting the intermediate thread at 1ts base, and a succeeding' tooth cutting below the base of the ilntermediate thread to complete the trou Y 9. A screw thread cutting die having initial thread cutting teeth forming a throat and cutting initial threads with a crest of the lead and approximating the final crests and an intermediate thread, a tooth cuttin off the intermediate threa and a succee g tooth. cuttin in the trough below the cut made by tooth.

10. A screw thread cutting die having teeth cutting an initial thread on a taper the crest of the final thread, said teeth orming an intermediate thread, a succeedin tooth cutting ofi said intermediate threa said cuttingofi tgoth having-glliiding sfurfiices coni tactin teoposln'g opeso teinitia threaci and a succeeding tooth completing the trough.

11. A screw thread cutting die having initial thread cutting teeth formingl an initial thread on a taper with a crest f0 owing the crest'of the final thread and an intermediate thread, a cutting tooth cutting the intermediate thread at its base, and a succeeding tooth cutting below the base, of the intermediate thread to complete the trough.

a 12. A screw thread cutting die having a tooth cutting an thread on a taper with a finala'edjappmximating the crest e cutting off of the final thread, said tooth also forming an intermediate thread, a succeeding tooth cutting ofl said intermediate thread and the $10 s leading to the intermediate thread, an succeeding teeth completing the trough from which the intermediate thread is removed.

13. A screw thread cutting die having a tooth cutting an initial thread on a taper with a final crest approximating the crest of the final thread, 881d tooth also forming an intermediate thread, a succeeding tooth cutting ofi said intermediate thread and the $10 es leading to the intermediate thread,

an succeeding teeth'completing the trough 15 from which the intermediate thread is removed comprising teeth making successive flat cuts in the trough.

In testimony whereof I have hereunto set my hand.

THORVALD PETERSEN. 

